1. Field of the Invention
The present invention relates to developing solution for a photoresist.
2. Discussion of the Related Art
In lithography techniques used in the manufacturer of LSI devices, the demand for highly dense and ultra fine circuits has increased. Also, the source of light used for light exposure has been shifting away from conventional mercury lamps, such as i rays (wavelength: 365 nm), to sources such as KrF excimer lasers (wavelength: 248 nm) and even ArF excimer lasers (wavelength: 193 nm), which have relatively shorter wavelengths.
Accompanying this shift of the light source, usable photoresists have been shifting from conventional compositions comprising a novolak resin and a naphtoquinonediazide compound to chemical-amplification type resist compositions having a light-induced acid-generating agent as the base resin. Further, usable base resins have been shifting from conventional phenol-based resins, such as novolak resins, to alicyclic compounds, which have greater transparency to ArF excimer lasers. Examples of such alicyclic compounds include terpene, bornene, tricyclodecane, and adamantane.
An aqueous solution of alkaline compounds is generally used as the developing solution for such photoresists. In manufacturing LSI devices, however, an aqueous solution of a non-metallic alkali compound is used, as these compounds do not deteriorate device properties. Quaternary ammonium hydroxides, such as tetramethylammonium hydroxide (hereinafter referred to as TMAH), are preferable.
Such developing solutions do not have sufficient wettability for the surface of a resist and can cause problems such as not sufficiently penetrating into fine patterns on the resist. Also, such developing solutions do not uniformly act on the entire surface of a substrate. To overcome these problems, Japanese Granted Application Publication No. 6-38159 suggested some alternative developing solutions, including one that is prepared by adding a nonionic surfactant to an aqueous solution of an organic basic salt.
When the alicyclic compound-based resin for the ArF excimer laser is used, however, hydrophobicity on the surface of the resist becomes notable, and wettability to the resist is insufficient (this is even when the above-mentioned developing solution is used). Furthermore, depending on the kind of surfactant used in the developing solution, dissolution selectivity among highly exposed portions and lesser exposed portions is insufficient. Further, when developing solution used for conventional phenol resin-based resists is applied to alicyclic compound-based resists, there are problems, such as resist residues remaining in the portions to be dissolved after developing. Consequently, the demand for a developing solution that is capable of forming fine patterns with alicyclic compound-based resists has increased.
It is an object of the present invention to provide developing solution having excellent wettability and dissolution selectivity. It is another object of the present invention to provide developing solution that does not produce dissolution residues after developing. It is yet another object of the present invention to provide developing solution that is capable of reliably forming fine patterns. It is a further object of the present invention to provide a method for developing a photoresist using this developing solution.
As a result of diligent and continuous studies in view of the objects above, the inventors have determined a developing solution for photoresists comprising an alicyclic amine compound and a non-metallic alkali compound that has excellent wettability and dissolution selectivity to alicyclic compound-based resists. The inventors have also determined that such developing solution does not produce dissolution residues and that it makes possible the reliable formation of fine patterns. The present invention has thereby accomplished the intended objects.
More detailed embodiments are now discussed using examples below.
In the present invention, a non-metallic alkali compound is used as a main component of the developing solution. Non-metallic alkali compounds have conventionally been used in developing solutions for alkali soluble resists, more particularly, as aqueous solutions of primary, secondary or tertiary aliphatic amines; aqueous solutions of heterocyclic amines comprising at least one atom selected from the group consisting of carbon, nitrogen, oxygen and sulfur atoms; and aqueous solutions consisting of quaternary ammonium hydroxides. Among these, quaternary ammonium hydroxides are particularly preferable because they are not volatile and because of their handling ease and excellent developing capabilities.
Usable primary, secondary and tertiary aliphatic amines include propylamine, butylamine, dibutylamine and triethylamine.
Usable heterocyclic amines include pyrrole, pyrrolidine, pyrrolidone, pyridine, morpholine, pyrazine, piperidine, oxazole and thiazole.
Usable quaternary ammonium hydroxides include tetramethylammonium hydroxide (TMAH), trimethylethylammonium hydroxide, triethylmethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, trimethyl (2-hydroxyethyl) ammonium hydroxide, triethyl (2-hydroxyethyl) ammonium hydroxide, and tripropyl (2-hydroxyethyl) ammonium hydroxide. Of these, TMAH and trimethyl (2-hydroxyethyl) ammonium hydroxide are particularly preferable. Quaternary ammonium hydroxides can be used individually, or in combinations of two or more.
The concentration of the non-metallic alkali compound in developing solution is appropriately selected so as to ensure a pH value between 13 and 14, depending on the kind of alkali being used. The concentration of the non-metallic alkali compound is preferably 0.1-10 wt %, and more preferably 1-5 wt %. When the concentration is lower than these ranges, dissolution requires a long time and development is prolonged. A concentration exceeding these ranges is not preferable because it degrades dissolution selectivity.
In addition to the aforementioned non-metallic alkali compounds, an alicyclic amine compound is also used as a main component of the developing solution of the present invention. The presence of the alicyclic amine compound in the developing solution serves to reduce the surface tension of the developing solution, to enhance the affinity of the developing solution with an alicyclic skeleton so that wettability to the resist increases, and to prevent the solution from producing residues in the portions to be dissolved upon development.
Examples of alicyclic skeletons of the alicyclic amine compounds used in the present invention include cyclo cyclic compounds, as represented by CnH2n (n=3 or higher), bicyclo cyclic compounds and condensed rings of these compounds, particularly rings such as cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane. It is also possible to use a compound having a bridging hydrocarbon introduced into these alicyclic compounds. Examples of such compounds include spiro rings such as spiroheptane and spirooctane, norbonyl rings, adamantyl rings, bornene rings, mentyl rings, terpene rings such as methane rings, steroid skeletons such as thujane, sabinene, thujone and cholesteric rings, camphor rings, isocamphor rings, sesquiterpene rings, santone rings, diterpene rings, and triterpene rings.
An alicyclic amine compound has one or more amino groups in its molecule. Usable amino groups include amino groups represented by xe2x95x90N.R1R2 (R1 and R2 are hydrogen atoms or hydrocarbons having from 1 to 4 carbon atoms) and aminoalkyl groups represented by xe2x95x90(CH2)nxe2x95x90N.R3R4 (n=1 to 6; R3 and R4 are hydrogen atoms or hydrocarbons having from 1 to 4 carbon atoms).
The above-mentioned alicyclic amine compounds can be compounds which have one or more of the groups selected from the group consisting of an alkyl group, a hydroxyl group, a hydroxyalkyl group and a nitro group, and which are directly bonded to the alicyclic skeleton at some other point in the molecular structure than the amino group.
Preferable examples of such alicyclic compounds having an amino group in the molecular structure include aminocyclobutane; aminocyclopentane; aminocyclohexane; aminocycloheptane; 1, 2-diamino cyclohexane; 1, 3-diaminocyclohexane; 1, 4-diaminocyclohexane; aminomethylcyclobutane; aminomethylcyclopentane; aminomethylcyclohexane; 1, 2-bis-(aminomethyl)-cyclohexane; 1, 3-bis-(aminomethyl)-cyclohexane; 1, 4-bis-(aminomethyl)-cyclopentane; 1, 4-bis-(aminomethyl)-cyclohexane; 1-methyl-2, 4-diaminocyclohexane; 1-methyl-2, 6-diaminocyclohexane; methylene-bis-4, 4xe2x80x2-aminocyclohexane and methylene-bis-2, 4xe2x80x2-aminocyclohexane; as well as bis-(aminomethyl)-tricyclodecanes, aminomethylnorbornenes, bis-(aminomethyl)-norbornenes and isophoronediamines. Among these, alicyclic compounds having a cyclohexane ringxe2x80x94such as 1, 3-bis-(aminomethyl)-cyclohexane and 1, 4-bis-(aminomethyl)-cyclohexanexe2x80x94which have good biodegradability and less biotoxicity, are particularly preferable.
The concentration of the alicyclic amine compound in the developing solution can be in the range of 0.001-5 wt %, but preferably 0.01-2 wt %, and more preferably 0.02-1 wt %. When the concentration is lower than these ranges, the surface tension does not decrease, while the affinity to resists does. When the concentration exceeds these ranges, the dissolution selectivity becomes insufficient. Two or more kinds of alicyclic amine compounds may be mixed for use as required.
In addition to the alicyclic amine compound and the non-metallic alkali compound, well-known additives to conventional developing solutions, such as surfactants, organic solvents, and anticorrosion agents, may be used in the developing solution of the present invention.
The developing solution of the present invention is particularly suitable for a chemical-amplification type resist composition used with an ArF excimer laser. This resist is an alicyclic resist comprising a resin having both a protecting group, which is introduced in an alkali-soluble resin containing alicyclic compounds, and a light-induced acid-generating agent. Examples of such resists include adamantyls (methacrylates), isobonylmethacrylate polymers and derivatives thereof. Protecting groups include t-buthyloxycarbonyl groups and t-butoxy groups, among others.
Usable acid-generating agents upon light-exposure include triphenylsulfoniumhexafluoroantimonate, isocyanurate halide, triazine halide, nitrobenzylsulfonicacid ester, diazonaphtoquinone-4-sulfonicacid ester, and alkylsulfonicacid ester.
The developing solution of the present invention can also be used for resists comprising a conventional aromatic alkali soluble resin and light-induced acid-generating agent, and for alkali-development type positive and negative resists comprising an alkali-soluble novolak resin and an azide compound-based sensitizing agent.
Usable methods of developing a photoresist generally include paddling, in which a developing solution is dropped onto the surface of a substrate; dipping, in which a substrate is dipped into a developing solution tank; and spraying, in which developing solution is sprayed onto a substrate. The developing solution of the present invention can be used in any of these methods. The temperature at developing is preferably in the range of 10-60xc2x0 C., and more preferably 15-30xc2x0 C.
In developing an alicyclic resist for an ArF excimer laser, excellent uniformity of development on the entire surface of the substrate and excellent dissolution selectivity are achieved using the developing solution and method of developing a photoresist of the present invention. As a result, fine device structures can be formed on the substrate.